Abstract: The phenomenon that some pesticides directly or indirectly remain in grains, vegetables, fruits, animal products, aquatic products, soils and water bodies after pesticides are applied in agricultural production.
1. Instruments: Agilent 6890N gas chromatograph (Agilent, USA), electronic capture detector (ECD), 7683 automatic sampler; ultrasonic cleaner; nitrogen blowing concentrator; food mashing machine; 2 mesh copper screen; chromatography column: The inner diameter is 10mm, the length is 350mm, the lower end is provided with a filter screen and a cock, and the upper end is connected with a 70mlSPE empty column with a cock as a container for containing eluent.
2 Instrument conditions: Capillary chromatography column: DB-XLB, column 301TI, inner diameter 0.25mm, liquid film thickness 0.25Ixm, inlet temperature 230 ~ C, deactivated glass liner and silanized glass wool inside, detector temperature 300oC, make-up gas (high-purity nitrogen) 30ml / min, column temperature as programmed temperature, initial temperature 110 ℃, keep 0.5min, 15 ℃ / min to 280oC, hold 2.0min, then 25 ℃ / min to 295oC, maintain 4.5min, carrier gas (high purity helium) flow rate 1.5mE / min, inlet split ratio 8: 1, injection volume 1.0.
3. Selection of extraction conditions: acetone and n-hexane (or petroleum ether) are commonly used for the extraction of organochlorine pesticides in food. For samples with low water content, non-polar solvents such as n-hexane or petroleum ether are used for extraction. Extracted with a mixed solvent composed of acetone, a sexual solvent. In the experiment, it was found that the polarity of cyclohexane as the elution solvent is close to that of n-hexane, which is also a non-polar solvent, and ethyl acetate is more polar. We tried to directly use the elution solvent ethyl acetate. Cyclohexane extraction The 6 organochlorine pesticides in tea can avoid the use of other solvents and introduce more pollution. Anhydrous sodium sulfate is added to remove trace water in tea, and ultrasonic extraction method is used to replace the commonly used oscillation method, which has high extraction efficiency and reduces the test time. Use an empty small column for solid phase extraction with a filter screen as an extraction container instead of a triangular flask or beaker to extract samples, and at the same time play the role of extraction and filtration. The SPE empty column has a small volume, the sample is relatively concentrated, and less solvent can be used , And avoid the use of funnels, filter paper, and reduce the number of sample transfers, which plays a role in reducing pesticide losses and improving recovery. In order to verify the feasibility of this extraction method, the residues of pesticide-containing samples extracted by this method were extracted according to the literature method. After the test, the contained components could not be detected, which shows that the extraction method is completely feasible.
4 The linear range and detection limit of each pesticide: after the test, the sample volume is 4.00g, the fixed volume is 2.0ml, and 1.0ml is absorbed and measured after purification treatment (the actual sample volume is 2.00g). The various pesticides are in the range of 0.025-0.50 The linearity is good in the range of mg / kg. When the content is high, the detection solution can be diluted and then measured. The detection limit is calculated by 2 times the baseline noise (S / N = 2).
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